Je
- Jenner, Edward
- Credited as the pioneer of smallpox vaccine, and is sometimes referred to as the "Father of Immunology"; his works have been said to have "saved more lives than the work of any other man".
- Jerk
- A vector quantity that specifies time rate of change of acceleration.
- Jerk Pump
- A fuel pump which injects fuel into the cylinder by action of a cam having a sharp nose.
- Jeroboam
- The name of a wine bottle equivalent to the volume of 4 standard bottles or 3 litres.
- Jet Engine
- An engine that discharges a fast moving jet of fluid.
- Jewellers Screwdriver
- A small precision screwdriver.